Naini Lake is a natural freshwater lake, of tectonic origin, located amidst Nainital city of Uttarakhand. It is lunar-shaped and has an outlet at the southeastern end. Naini Lake is one of the four lakes in Kumaon hills, the three other being Sattal Lake, Bhimtal Lake and Naukuchiyatal Lake. Balia Nala is the main feeder-stream of the lake. Other than this, 26 major drains, including the three perennial ones, feed it.

Increasing population, unplanned growth of human settlements and tourists together appear to have taken a toll of the beautiful lake that gives the hill resort of Nainital its name. According to a recent study conducted by D K Pandey of the Dehradun-based Forest Research Institute, the water quality of the Naini lake has been steadily deteriorating and is highly polluted due to the addition of exogenous wastes, as a result of more than 37 per cent increase in human population in the catchment area of the lake and too many tourists. Also, high siltation resulting in reduction of lake depth, the depth of lake have reduced from its original depth of 29 m in 1871 to only 13m in 2007.

With an increasing amount of sewage, municipal and domestic wastes finding their way into the lake, the quantity of organic matter in its waters has risen sharply. This has starved the lake of cleansing oxygen, pushing up the biological oxygen demand (BOD) -- by over 20 times over a 10-year period. From 15.5 parts per million (ppm) in 1981, the BOD shot up to 357.23 ppm in 1991. Similarly, the concentration of free carbon dioxide in the lake --- which depends on the population of aquatic organisms and the type of waste added to the water ecosystem --- has increased by 670 per cent over the same period.

In 1993, petition was filed by Dr. Rawat, who is a member of social action group called 'Nainital Bachao Samiti', who approached the Court seeking its assistance to pass such orders and give such directions as would prevent further pollution of already suffocating Nainital. By an order dated 14.7.1994, the Court had felt it fit, after having gone through the petition, to appoint a Commissioner for local inspection and to give report on various important points. A perusal of that report shows that on local inspection it was found that the lake has turned dark green with an oily surface and is now full of dirt, human faeces, horse dung, paper polythene bags and all sorts of other waste. Most of the sewer lines, which leak, ultimately disgorge the faecal matter into the lake through the drains, which open into it. One more petition was filed in 2006, in which a panel chaired by the state's chief conservator of forests directed that construction at Hanuman Garhi Park be stopped, which is at hillock.

1995: Supreme court passed directions for proper maintenance of the Ballia ravine, banning of construction of multi-storied group housing societies in Nainital township, prevention of sewage and other pollutants from entering the lake. But still the authorities have okayed new projects.

2002: Roorkee-based NIH ( National institute of hydrology ) is working on the restoration of the Naini Lake in under a Rs 50 crore restoration programme sponsored by the Ministry of Environment and Forests. The Conservation and Management Plan evolved by NIH is not only lake centric but also proposes to tackle the immediate periphery of the lake which contributes an adverse impact on the lake.

2004: NIH working on means clean the lakebed of accumulated pollutants.

2006: Another petition filed by Rawat seeking a ban on building in eco-fragile areas, that is, the catchment area of the lake. The public also protested. As a result, a panel chaired by the state's chief conservator of forests directed that construction at Hanuman Garhi Park be stopped, which is at hillock. This construction would have destroyed Himalayan oaks, which store water and release it for springs that feed the lake. There were 250 springs before 1950 out of these, 30 remain by today. No action has been taken to stop construction elsewhere.

2008: The authorities implemented scientifically designed waste management project in order to restore the lost grandeur of the Naini Lake. Bio-manipulation project is being implemented in the lake after the lake's ecosystem got cleaner. Under this project, 35,000 Mahashir fish have already been released into the lake.

In December, the residents switched to scientifically designed garbage disposal system. Under the project named Mission Butterfly, the sweepers collect waste from each and every household and then directly transfer it to the compost pits where it is converted to manure. Through this there can be control on that was falling in the lake. Students are taught in school regarding garbage disposal and lake conservation.

2009: The Supreme Court has asked an environmentalist to approach the Uttarakhand High Court to stop large-scale illegal constructions and felling of trees in Nainital to preserve the beauty of the town and the main lake by strictly implementing an earlier order of the apex court. The apex court's order came after senior counsel Vivek Singh Attri, appearing for the petitioner, said multi-storeyed group housing societies and commercial complexes were coming up in the town with official connivance. Trees were also being cut in a big way in utter violation of the SC order and the Forest (Conservation) Act, 1980.
It gave the order that “ Multi-storeyed group housing and commercial complexes have to be banned in the town area of Nainital. Building of small residential houses on flat areas could, however, be permitted." The court had also asked the state to make illegal felling of trees a cognizable offence and restrict vehicular traffic on the Mall.

June 2009: Bio-manipulation continues

August 2009: Civic authorities in Naintal launched a fresh demolition drive of illegal
buildings and structures, which were posing a threat to the environment and the lake.